The present invention relates to a method of manufacturing a negative resistance semiconductor device structure known as a thyristor having a pnpn junction. Particularly, the invention relates to a thermo-sensitive switching element which utilizes the thermal characteristics of a thyristor.
An example of a thermo-sensitive thyristor structure switching element is shown in FIG. 1. A thyristor is usually shown schematically as a three-electrode element having anode, cathode and gate electrodes. However, internally it is a compound element made up of an npn transistor and a pnp transistor.
This structure will be described with reference to FIG. 1 in more detail. In FIG. 1, reference character 1 designates the anode region of the thyristor and which acts as the emitter of the pnp transistor. A region 2 is employed as the gate of the thyristor, the base of the pnp transistor or the collector of the npn transistor and is hereinafter referred to as "an n base region" when applicable. A region 3 is employed as the gate of the thyristor and acts as the collector of the thyristor and acts as the collector of the pnp transistor or the base of the npn transistor and is hereinafter referred to as "a p base region" when applicable. A region 4 is the cathode region of the thyristor and acts as the emitter of the npn transistor. Further in FIG. 1, reference numeral 5 designates an electrode formed with aluminum or the like, 6 a surface protecting oxide film of silicon dioxide (SiO.sub.2) or the like, 7 an isolation layer, and 8 a defect layer which is intentionally formed by implantation of argon ions in the collector junction.
In operation, the thyristor structure element as described above acting as a thermo-sensitive switching element is placed in thermal contact with an object whose temperature is to be measured and a DC voltage or an AC voltage is applied between the anode 1 and the cathode 4 in such a manner that the anode is at a positive voltage while the cathode is at a negative voltage. When the temperature of the object reaches a predetermined value, the switching element is operated. That is, the "off" or high resistance state between the anode 1 and the cathode 4 changes to the "on" or low resistance state.
Such a thermo-sensitive switching operation can be carried out with an ordinary thyristor. However, the use of an ordinary thyristor is limited because its switching temperature is very high. In order to eliminate this limitation and to thus make the thyristor structure element more useful as a thermo-sensitive switching element, the following techniques have been employed to cause the switching element to operate at a lower temperature. First, the common base current amplification factors (.alpha.npn) and (.alpha.pnp) of the npn transistor regions 2, 3 and 4 and the pnp transistor regions 1, 2 and 3 have been increased. Secondly the reverse leakage current I.sub.0 in the pn junction J.sub.2 formed by the n base region 2 and the p base region 3 was increased. Alternatively, the temperature dependencies of the factors (.alpha.npn), (.alpha.pnp) and I.sub.0 have been increased.
However, if the common base current amplification factors (.alpha.npn) and (.alpha.pnp) are excessively increased, then the switching characteristic tends to become unstable and accordingly the switching element may be operated erroneously by external noise. Therefore, in general, the technique of increasing the leakage current I.sub.0 in the pn junction J.sub.2 has been preferred. In an example of such a technique, as shown in FIG. 1, the defect layer 8 is formed by implantation of argon ions into the pn junction J.sub.2. This defect layer 8 acts as a recombination center for forming a recombination current to thereby increase the leakage current. The thermo-sensitive switching temperature can be reduced to a low value by increasing the leakage current as described above. In addition, the amount of leakage current can be readily controlled because the amount of argon ions implanted can be controlled with a high accuracy.
On the other hand, the thermo-sensitive characteristic of the thermo-sensitive thyristor is determined by the mutual relation of the reverse leakage current I.sub.0 of the pn junction J.sub.2 and the common base current amplification factors (.alpha.npn) and (.alpha.pnp). Therefore, in order to manufacture a thermo-sensitive thyristor having a desired characteristic with a high accuracy, it is necessary that the common base current amplification factors (.alpha.npn) and (.alpha.pnp) be correctly determined before argon ion implanation is carried out. However, on a semiconductor wafer, it is considerably difficult to measure the values (.alpha.npn) and (.alpha.pnp) with extremely small currents and, even if the measurement can be achieved, the measurement results are very low in accuracy. Therefore, the thermo-sensitive characteristic of the manufactured thermo-sensitive thyristor can be expected unavoidably to deviate from the desired characteristic.
Accordingly, an object of the invention is to provide a method of manufacturing semiconductor elements having a desired thermo-sensitive characteristic with a high yield and in which all of the above-described difficulties accompanying a conventional thyristor structure thermo-sensitive switching element manufacturing method have been eliminated.